Combine the sliced rhubarb, quartered strawberries, honey, and vanilla extract in a bowl and toss gently until the fruit is evenly coated. The honey will start to dissolve and release juice from the strawberries—this creates the filling's syrupy base. Transfer the mixture to an 8x8 inch or 9x9 inch baking dish, spreading it in an even layer.

In a separate bowl, combine the oats, brown sugar, and cinnamon, stirring until evenly mixed. Cut the butter into small cubes and add it to the dry mixture. Using your fingers or a pastry cutter, work the butter into the oats until the mixture resembles coarse breadcrumbs with some pea-sized clumps remaining. I like to leave some larger butter pieces throughout—they create pockets of crispy texture as they bake. Don't overmix or the topping will become dense.

Preheat your oven to 350°F. Once the oven reaches temperature, evenly distribute the crisp topping from Step 2 over the fruit filling from Step 1, spreading it gently with your fingers but leaving it slightly uneven—this creates texture when baked. Bake for 40 minutes until the topping turns golden brown and the fruit filling is bubbling around the edges. You'll see some of the rhubarb-strawberry juices peeking through the topping, which is exactly what you want.

Remove the crisp from the oven and let it rest for 5-10 minutes before serving. This resting time allows the filling to set slightly so it won't be runny, but serves best while still warm. Scoop into bowls and serve as-is or with a dollop of Greek yogurt or whipped cream if desired.